1. Field of the Invention
The present invention relates to a geared motor, particularly, a geared motor provided with a geared rotating axle for transmitting speed reduced rotation of a rotor of the motor.
2. Description of Related Art
A geared motor such as a motor for driving a wiper is typically provided with a gear for transmitting speed-reduced rotation from a rotating axle, for example, an armature shaft, of the motor, while also changing the direction of rotation. This type of geared motor for driving a wiper is comprised of a gear section in which reduction gears are disposed, provided adjacent to a motor section in which a rotor, a stator and a rotor axle are disposed.
A worm gear which is comprised of a worm and a gear wheel is generally used as a reduction gear in the gear section. The worm is connected to the rotating axle of the rotor in the motor section, and the worm is engaged with the gear wheel. The gear wheel has a rotating axle to which a crank arm for driving the wiper is connected.
The motor drives the wiper as follows: when the rotor in the motor section rotates, the worm rotates with the rotor and the gear wheel is rotated by the worm. Accordingly, the crank arm for driving the wiper is driven.
A connection member is indispensable to this type of geared motor, for connecting the rotating axle of the rotor in the motor section with a rotating axle in the gear section, such as the worm part of a worm gear used for transmitting speed reduced rotation in the above example. Further, it is necessary for the connection member to transmit rotation while absorbing any oscillation due to eccentricity of the two rotating axles with respect to each other. To satisfy these conditions, a geared motor using a flexible coupling as the connection member is known to us, for example, U.S. Pat. No. 4,170,847.
In this geared motor using a flexible coupling, oscillation is reduced and rotation is reliably transmitted from the first to the second of the two rotating axles, since the oscillation due to the eccentricity of the two rotating axles is absorbed by the flexible coupling portion which is made of rubber.
However, in this type of geared motor there exists a problem in that there is no provision for longitudinally acting thrust force which acts on both the rotating axle of the rotor in the motor section and the rotating axle of the speed reduced rotation transmitting gear in the gear section, since the geared motor uses an ordinary flexible coupling whose object is only to transmit the rotation while absorbing oscillation due to eccentricity of the two rotating axles. Therefore, there is a possibility of the life-expectancy of the flexible coupling being reduced due to vibration occurring along the longitudinal thrust axis and affecting the connecting portions of the rotating axle of the rotor and the rotating axle of the speed reduced rotation transmitting gear, and the connection member, namely, the flexible coupling. Also, it is impossible to accurately adjust the device for reduction of vibration in the thrust direction since the rotating axle of the rotor and the rotating axle of the speed reduced rotation transmitting gear are connected to each other along the axis of thrust through an elastic body.